The Wnt gene family encodes secreted glycoproteins that play diverse roles during vertebrate and invertebrate development and have been associated with tumor formation in mice and humans. Analyses of Wnt signaling in multiple tissues and species have led to the hypothesis that Wnt proteins use similar signaling mechanisms. However, a critical question for understanding Wnt activity is how specificity between different family members is achieved. This application proposes to address this issue by examining the signaling pathways of two Wnt proteins during Drosophila development. Four Wnt genes have been identified in Drosophila, but only wingless, the ortholog of Wnt-1, has been well characterized. A second Wnt gene, DWnt-4, has been shown to be expressed in a partially overlapping pattern with wingless and the two genes influence some of the same processes but in distinct ways. Three specific aims are presented to test the hypothesis that Wnt genes elicit specific effects by interacting with both shared and unique signaling components and to identify signaling components that are unique to DWnt-4. The first specific aim is to determine the function of DWnt-r through generation of loss-of-function mutations and phenotypic analysis. The second specific aim is to identify genes that specifically interact with D Wnt-4 using genetic enhancement and suppression screens. The third specific aim uses in vitro experiments involving transient transfection of tissue culture cells to ask whether previously identified components of the wingless signaling pathway can mediate Dwnt-4 signaling.